Brucellosis is one of the world's most frequent zoonotic diseases with over 500,000 new human infections every year. Brucella abortus strain 19 vaccine, developed in the 1930s, is the principal vaccine used to prevent transmission of brucellosis from cattle to humans worldwide and in Brazil. The mechanisms that mediate protection by strain 19 are poorly understood. Host mechanisms of innate immunity induced by the vaccine that control infection remain obscure. Indeed, the vaccine contains several properties that are inhibitory to host immunity. Our research group was the first to implicate the role of inflammasome receptors in the control of Brucella abortus infection. Further, our team has demonstrated that IFN-aR KO mice are more resistant to infection suggesting that type I IFN signaling favors Brucella multiplication in the host. Therefore, our long-term goal is to resolve the conundrum of how Brucella activates innate immune components that results in host resistance versus bacterial subversion of the immune response. Brucella spp are one of the few bacterial pathogens that use the endoplasmic reticulum (ER) as its replicative niche. The Unfolded Protein Response (UPR) is a conserved signaling pathway in eukaryotes that mediates cellular adaptation to protein-folding stress in the ER. The UPR also modulates innate immunity. Recently, our collaborators have demonstrated that Brucella induces the UPR that enables its intracellular replication. Based on these compelling preliminary data, we propose to test the central hypothesis that Brucella abortus strain 19 activates protective innate immune mediators and triggers the UPR to secure intracellular replication. Further, we propose that the strain 19 induced UPR regulates cytokine production. Our specific aims are to determine whether: 1) NLRP3 inflammasome activation and IL-1? secretion induced by Brucella requires the UPR; 2) the bacterial virulence factor ? TcpB that modulates host cell microtubules activates the NLRP3 inflammasome and IL-1? and 3) the UPR activated by Brucella abortus strain 19 regulates STING expression and type I interferon production to facilitate bacterial persistence. We believe that our approach will shed light on the mechanisms of immunity against this important human and animal pathogen. Additionally, critical information gained from these specific aims will begin to bridge the gap between what we know about mechanisms of protection induced by B. abortus vaccine strain 19 and how bacterial persistence is regulated. Finally, the investigators on this proposal have a strong track record in brucellosis research and a unique combination of key expertise in whole animal models, immunology, human brucellosis, cell biology, and analysis of the UPR.